When a user equipment (UE) is performing a Voice over Internet Protocol (VOIP) service in a packet switched (PS) domain of a System Architecture Evolution (SAE)/Long Term Evolution (LTE) network, an LTE voice service based on an IP multimedia subsystem (IMS) network is referred to as a VoLTE service. The service has an independent access point name (APN), and the UE creates a corresponding packet data network (PDN) connection. A default bearer is QCI 5 and is used to bear Session Initiation Protocol (SIP) signaling. When the UE has a voice service, a policy control and charging (PCC) architecture triggers a network side to create a dedicated bearer QCI 1 to bear voice.
After a High Speed Packet Access (HSPA) network is deployed, IP voice based on an IMS network is gradually applied, and this kind of voice application is generally referred to as a VoHSPA service. The HSPA network is formed by upgrading a previous UMTS Terrestrial Radio Access Network (UTRAN). A serving general packet radio service (GPRS) support node (SGSN) on a core network side may be an S4 SGSN connected to a serving gateway (SGW), or may be a Gn/Gp SGSN connected to a gateway GPRS support node (GGSN).
As shown in FIG. 1a, when UE is attached to an LTE network, serving network elements of the LTE network separately are a mobility management entity (MME), an SGW, and a PDN gateway (PGW) that are in an area 1 (Area 1). After the UE moves from the area 1 to an area 2 (Area 2), the PGW is anchored and unchanged. That is, although the UE moves from the Area 1 to the Area 2, the PGW is still anchored in the Area 1.
Similarly, as shown in FIG. 1b, when UE is attached to an HSPA network, serving network elements of the HSPA network separately are an SGSN, an SGW, and a PGW that are in an Area 1. After the UE moves from the Area 1 to an Area 2, the PGW is anchored and unchanged. That is, although the UE moves from the Area 1 to the Area 2, the PGW is still anchored in the Area 1.
Similarly, as shown in FIG. 1c, when UE is attached to an HSPA network, serving network elements of the HSPA network separately are an SGSN and a GGSN that are in an Area 1. After the UE moves from the Area 1 to an Area 2, the GGSN is anchored and unchanged. That is, although the UE moves from the Area 1 to the Area 2, the GGSN is still anchored in the Area 1.
For example, for a VoLTE voice service, a SIP signaling stream and a voice stream are represented by the second dashed line in FIG. 1a, and there is a detour on the SIP signaling stream and the voice stream, which is the same for a VoHSPA service, thereby affecting voice service experience of a user.
On the other hand, when roaming between different public land mobile networks (PLMN), the user equipment still performs a voice service by using an anchor gateway of an original PLMN. However, generally different operators cannot interwork; therefore, the user equipment cannot smoothly perform the voice service, which also affects the voice service experience of the user.